Provisioning New Prebuild Workspaces

[SasSwart]

Prebuilds are normal workspaces, except for a few attributes that identify them as prebuilds. These attributes need to be added to the workspace provisioning process, so that we can mark workspaces as prebuilds. Relevant changes in the workspace builder and provisionerd server need to be introduced to facilitate identifying a workspace as a prebuild.

Agent reinitialisation is a separate issue. For this issue, we are only concerned with changes to workspace provisioning up to but excluding agent reinitialisation